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servation. About the same time an equally
beneficial step was the employment of the
telescope as a pointer; not the Galilean with
concave eye-piece, but with a magnifying
glass to examine the focal image, at which
also a fixed mark could be placed. Kepler
was the first to suggest this. Gascoigne was
the first to use it. Huyghens used a metal
strip of variable width in the focus, as a mi-
355